Conventional lawn and garden tractor vehicles are well adapted for use as mowing vehicles. They typically include four ground engaging wheels, the rear pair of wheels being driven and the front pair of wheels being pivotable by the operator to steer the vehicle. Conventional lawn tractors include an engine mounted at the front of the vehicle. An operator station includes a seat upon which the operator sits behind the engine. Conventional lawn tractors such as these having front mounted engines are well accepted by residential consumers. These vehicles are quite maneuverable and therefore perform well mowing grassy areas such as residential lawns. The steerable front wheels allow the vehicle to execute relatively sharp turns of relatively small radius, but generally do not allow zero radius turns or spin turns. In a zero radius turn a vehicle executes a turn about a vertical axis passing through one of its rear driven wheels. In a spin turn a vehicle executes a turn about a vertical axis passing through the centerline of the vehicle. Conventional lawn tractors have the disadvantage of being less maneuverable than vehicles that are capable of executing zero radius turns or spin turns.
It is known to provide mowing vehicles that execute zero radius turns and spin turns. One such type of vehicle provides independently controlled hydrostatic drives which can drive respective left and right drive wheels at different speeds to cause the vehicle to execute a turn to the side of the slower wheel. Left and right control levers are operatively coupled with the respective left and right hydrostatic drive mechanisms and can be manipulated by the operator seated in the operator station for controlling the speed of the respective drive wheels. As the operator pivots the right control lever forwardly the hydrostatic drive for the right drive wheel causes the right drive wheel to rotate in a forward direction. The farther the operator pivots the lever forwardly the faster the drive wheel will rotate. If the operator pivots the right control lever rearwardly, the right drive wheel will be driven in reverse. The farther the operator pivots the lever rearwardly, the faster the right drive wheel will rotate in reverse. The left drive wheel operates in similar fashion in response to the operator manipulating the left control lever. When the operator pivots both levers forwardly the same amount, both drive wheels rotate forwardly at the same speed and the vehicle is propelled forwardly in generally a straight line. To execute a turn during forward travel the operator can pivot one lever rearwardly with respect to the other lever to execute a turn in that direction. For example, with both levers pressed forward to the same degree for straight forward travel, the operator can pull back the left control lever slightly with respect to the right control lever, which will slow the left drive wheel relative to the right drive wheel, and therefore the vehicle will execute a turn to the left.
When the vehicle is stationary, the operator can pivot one control lever forwardly while keeping the other in its upright neutral position. This will cause one drive wheel to be driven forwardly while the other drive wheel remains stationary, and therefore the vehicle will execute a zero radius turn, which is a turn about a vertical axis passing through the stationary drive wheel.
The operator of such a vehicle can also execute a spin turn by pivoting one control lever forwardly and the other control lever rearwardly. This causes one drive wheel to be driven forwardly and the other drive wheel to be driven in reverse, which causes the vehicle to pivot or turn about a vertical axis located somewhere between the two drive wheels. If both drive wheels are rotating at equal and opposite directions, then the vehicle will execute a turn about a vertical axis passing through the centerline of the vehicle equidistant between the two drive wheels.
Conventional lawn mowers of this type have the advantage of being highly maneuverable. They can execute zero radius turns or spin turns. This tight turning is particularly advantageous when an operator comes to an edge of a yard during mowing operations and wants to turn around and mow in the opposite direction. The operator can simply execute a zero radius turn and begin mowing back in the opposite direction. Furthermore, spin turns are advantageous when mowing in tight spaces or when maneuvering out of confined spaces such as a storage garage. The vehicle can be driven straight into a storage building, and then when it is time to drive out of the building the operator can execute a spin turn and drive forward out of the building.
Conventional lawn mowers of this type having independently controlled hydrostatic transmissions for each drive wheel can be relatively difficult for many people to operate. The left and right control levers can be somewhat difficult for first time operators to become comfortable using. Making an accurate turn during mowing operations alongside structures such as flower beds can be difficult for many operators using the left and right hand control lever system. Since the controls are so different from conventional steering and foot pedals such as are found in automobiles, many customers of mower vehicles will not choose to purchase a vehicle having left and right control levers as is provided on typical zero turning radius mower. Because of leakage and other small differences in the two hydrostatic transmissions on each vehicle, it may be difficult for an operator to drive the vehicle in a straight line using the control levers. The operator may have to hold the left and right control levers at slightly different forward positions to drive the vehicle in a straight line. If the operator can not locate the proper locations the levers must assume in order to travel forward in a straight line, the operator will have to constantly make corrections and steer the vehicle back to the intended path of travel. Many operators find these constant adjustments difficult and bothersome.
Conventional zero turning radius mowers position the engine to the rear of or directly over the rear drive wheels, and therefore there is no large amount of weight carried far in front of or behind the rear drive wheels that has to be swung about during a turn. The position of the engine over the rear drive wheels of conventional zero turn radius mowers also helps place a large portion of the vehicle weight on the drive wheels, which will increase traction at the drive wheels and thereby enhance the vehicle's ability to execute turns.
Typical dual hydrostatic zero turning radius mowers have a mower deck that is mounted in front of the vehicle or between the front and rear pairs of wheels. The engine is mounted to the rear of the vehicle, and the operator station and seat are positioned generally in front of the engine. Because of its configuration, this type of vehicle can be perceived by the average consumer to be quite different from a conventional lawn tractor having its engine mounted at the front of the vehicle and the mower deck mounted between the front and rear pairs of wheels. Therefore, some consumers might not purchase one of these dual hydrostatic types of vehicles because it does not meet his expectations of what a lawn mowing vehicle should be.
Another type of transmission allows a vehicle to execute zero radius turns and spin turns. Military tank vehicles and other tracked vehicles have been provided with a dual differential transmission capable of zero radius turns and spin turns. This type of drive and steer transmission is described in the articles entitled Tanks And Dozers Turn On A Dime With New All-Gear Steering, and Tank-Steering Mechanisms. The transmission includes a driving portion having a driving differential which receives rotational power from the vehicle power source for propelling the vehicle during operation. The driving portion includes a drive control which can be operatively engaged by the operator for varying the speed and forward/reverse direction of the vehicle. The transmission also includes a steering portion having a steering differential. The steering portion includes a steering control that can be operatively pivoted by an operator for executing turns. The steering portion is operatively coupled with the driving portion such that when the steering input is engaged by the operator to execute a turn the steering portion increases the speed of the track on one side of the vehicle and proportionately decreases the speed of the track on the other side of the vehicle. In this manner the vehicle executes a turn. When the vehicle is stationary, the operator can engage the steering input, which will cause the track on one side of the vehicle to be driven forwardly, and the track on the other side of the vehicle to be driven rearwardly at the corresponding speed. This causes the vehicle to execute a spin turn.
As described in the article entitled Tank-Steering Mechanisms, a different transmission having planetary gear arrangements functions in a manner similar to the dual differential type of drive and steer transmission described above. This other type of transmission, hereinafter referred to as a planetary type drive and steer transmission, also includes a driving portion having a driving control, and a steering portion having a steering control. The steering portion interacts with the driving portion to increase the speed of the tracks on one side of the vehicle and correspondingly decrease the speed of the tracks on the other side of the vehicle.
These types of drive and steer transmissions allow the vehicle to be highly maneuverable, and allow the vehicle to execute zero radius turns and spin turns. These drive and steer transmissions are typically provided on heavy duty vehicles such as military tanks, bulldozers, and other large tracked vehicles.
Conventional drive and steer transmissions are not commercially available on front engine lawn tractor vehicles. The use of a conventional dual differential or planetary type drive and steer transmissions on a conventional front engine lawn tractor would not provide the steering and handling characteristics that are generally required by operators of front engine lawn tractors. For example, if a typical conventional drive and steer transmission were coupled with a front engine lawn tractor, the steering might be relatively aggressive such that small turns of the steering wheel might result in sharp turns. And many conventional drive and steer transmissions allow relatively sharp turns, or even spin turns, to be executed at relatively high speeds, which might cause a lawn tractor to tip over. These operating characteristics may be desirable for a military tank that is specially designed for stability during tight turns at high speeds, and which are operated by highly skilled and trained personnel. But these operating characteristics are generally not desirable for a front engine lawn tractor such as are used for residential mowing purposes.
Furthermore, conventional drive and steer transmission such as those used on tracked vehicle would generally not be effective at swinging the relatively large weight of the front of a front engine lawn tractor to the side in order to execute a vehicle turn. A front engine lawn tractor has a relatively large amount of weight supported by the front end of the vehicle. If a conventional drive and steer transmission were coupled with the rear wheels of a front engine lawn tractor, the rear drive wheels would be driven at different speeds in order to cause the vehicle to execute a turn. Therefore the vehicle would effectively be turned from the rear of the vehicle as the rear ground wheels rotate in engagement with the ground at different speeds. During execution of a turn the front of the vehicle would have to be swung to one side by the rear drive wheels. The relatively large weight carried at the front of the vehicle associated with the forward location of the engine would be relatively difficult to swing to one side to execute a turn. This is because the weight of the engine is located so far from the rear wheels which are effectively steering the vehicle. An analogous situation is a shopping cart with front caster wheels and which is pushed from behind in conventional fashion. The more weight that is placed in the far front of the shopping cart, the harder it become for the person pushing the cart to turn the cart from the rear. A conventional lawn tractor with a front mounted engine is similarly difficult to turn by applying steering force at the rear of the vehicle. It would be relatively difficult to swing the heavy front end of a front engine lawn tractor around to execute a turn by driving the rear wheels at different speeds. Tracked vehicle such as tanks which use conventional drive and steer transmissions generally do not encounter this problem since the tracks extend generally the entire length of the vehicle. In other words, tanks do not have a large weight located far in front of the tracks that must be swung about in order to execute a turn. Therefore, conventional drive and steer transmissions as described above which are typically used on tracked vehicles such as tanks are generally not suitable for use with a front engine lawn tractor.
Therefore, it would be desirable to provide a front engine lawn tractor that has improved maneuverability so that the vehicle can execute tighter turns and more easily operate in confined spaces. It would be desirable for such a vehicle to have the characteristics of a front engine lawn tractor such that the vehicle will meet residential consumers' expectations of a lawn mower vehicle. If such a vehicle is a front engine type vehicle, parts and manufacturing methods could be used that are common with conventional front engine lawn tractors, which would reduce the cost of manufacturing such a vehicle. It would be desirable for such a vehicle to have a conventional steering wheel and foot pedal controls that most consumers are familiar and comfortable with. It would be desirable for such a vehicle to be capable of executing zero radius turns and spin turns. Such a vehicle would be highly maneuverable. It would be desirable for such a vehicle to have steering and handling characteristics that are similar to those of a conventional lawn and garden tractor. This would allow an operator to be familiar and comfortable with the performance characteristics of the vehicle.